Coordinated Capacitor Voltage Balancing Method for Cascaded H-bridge Inverter with Supercapacitor and DC-DC Stage

Cascaded H-bridge inverter(CHBI) with supercapacitors(SCs) and dc-dc stage shows significant promise for medium to high voltage energy storage applications. This paper investigates the voltage balance of capacitors within the CHBI, including both the dc-link capacitors and SCs. Balance control over the dc-link capacitor voltages is realized by the dcdc stage in each submodule(SM), while a hybrid modulation strategy(HMS) is implemented in the H-bridge to balance the SC voltages among the SMs. Meanwhile, the dc-link voltage fluctuations are analyzed under the HMS. A virtual voltage variable is introduced to coordinate the balancing of dc-link capacitor voltages and SC voltages. Compared to the balancing method that solely considers the SC voltages, the presented method reduces the dc-link voltage fluctuations without affecting the voltage balance of SCs. Finally, both simulation and experimental results verify the effectiveness of the presented method.

Model Predictive Control for Cascaded H-Bridge PV Inverter with Capacitor Voltage Balance

We designed an improved direct-current capacitor voltage balancing control model predictive control(MPC)for single-phase cascaded H-bridge multilevel photovoltaic(PV)inverters.Compared with conventional voltage balanc-ing control methods,the method proposed could make the PV strings of each submodule operate at their maximum power point by independent capacitor voltage control.Besides,the predicted and reference value of the grid-connected current was obtained according to the maximum power output of the maximum power point tracking.A cost function was con-structed to achieve the high-precision grid-connected control of the CHB inverter.Finally,the effectiveness of the proposed control method was verified through a semi-physical simulation platform with three submodules.

THREE-PHASE BRIDGE INVERTER FOR 9kW DOUBLY SALIENT PERMANENT MAGNET MOTOR

The three-phase bridge inverter is used as the converter topology in the power controller for a 9 kW doubly salient permanent magnet （DSPM） motor. Compared with common three-phase bridge inverters, the proposed inverter works under more complicated conditions with different principles for special winding back EMFs, position signals of hall sensors, and the given mode of switches. The ideal steady driving principles of the inverter for the motor are given. The working state with asymmetric winding back EMFs, inaccurate position signals of hall sensors, and the changing input voltage is analyzed. Finally, experimental results vertify that the given anal ysis is correct.

A new three-phase 5-level current-source inverter

The new three-phase 5-level current-source inverter (CSI) proposed in this paper was developed by connecting three separate single-phase 5-level CSIs in series, and its operational principle was analyzed. There are two major problems existing in current-source multilevel inverters, one is the complex PWM control method (2-logic to 3-logic conversion), and the other is the problem of current-unbalance between different levels. A simple current-balance control method via DC current feedback is applied in each single-phase 5-level CSI cell to implement the current-balance control between different levels. And to reduce the output current harmonics, POD PWM control technique was used. Simulation and experimental results showed that this new three-phase 5-level CSI topology operates correctly.

Symmetrical dynamical characteristic of peak and valley current-mode controlled single-phase H-bridge inverter

Complex dynamical phenomenon was studied in the single phase H-bridge inverter which was controlled by either a peak current or a valley current. The state functions and the discrete iterative map equations were established to analyze the dynamical phenomenon in the single phase H-bridge inverter. The dynamical characteristics of the single phase H- bridge inverter, such as time domain waveform diagram, bifurcation diagram, and folding map, were obtained by using the numerical calculation when the circuit parameters varied in specific range. Moreover, the simulation results were obtained by using the OrCAD-PSpice software to validate the numerical calculation. Both the numerical calculation and the circuit simulation show that the symmetrical dynamical phenomenon occurs in the single phase H-bridge inverter controlled by the peak current or the valley current.

Control strategy of LCL-type three-phase photovoltaic grid connected inverter

The grid-connected inverter with LCL filter has the ability of easily attenuating high-frequency current harmonics. However, its suppression effect on the background harmonics in grid voltage is limited. A control strategy is presented, which is composed of an inner loop of capacitor current feedforward, an outer loop of grid-current feedforward and feedforward of grid voltage. The limitations and steps of parameters design for LCL filter are analyzed. Meanwhile, the capacitor current loop is employed to damp the resonant peak caused by the LCL filter and enhance the stability. The properties of different controllers are analyzed and compared, thereinto quasi-proportional-rasonant (PR) controller realizes the control with zero steady-state error of AC variables in static coordinates. In order to suppress the current distortion effected by the background harmonics in grid voltage, the feed-forward function is calculated for the grid-connected inverter with an LCL filter. After simplifying the block diagram, a full-feedforward control strategy for grid voltage is proposed. Theoretical analysis and Matlab/Simulink simulation results show that the proposed method has the advantages of high steady accuracy, fast dynamic response and strong robustness.

The Research of Three-phase Boost/Buck-boost DC-AC Inverter

This paper presents a new inverter based on three-phase Boost/Buck-boost single-stage inverter. The basic configuration of the new topology and their fundamental principle are firstly introduced, the method of design double-loop controller and sliding mode controller are clarified, analyzed and compared in the following. Finally the validity and feasibility of the new topology are tested by simulation. The results indicate that regulation of the voltage transfer ratio and output frequency can be realized optionally by the new converter, furthermore the harmonic distortion of waveform is low. So the inherent drawback of low voltage transfer ratio of traditional converter is effectively settled. This study may provide inspiration for further engineering application.

The Control Technology Research of the Z-source Three-phase Four-bridge Arm Inverter

Z-source inverter can boost the voltage of the DC-side, allow the two switches of the same bridge arm conducting at the same time and it has some other advantages. The zero-sequence current flows through the fourth leg of the three-phase four-leg inverter so the three-phase four-leg inverter can work with unbalanced load. This paper presents a Z-source three-phase four-leg inverter which combines a Z-source network with three-phase four-leg inverter. The circuit uses simple SPWM modulation technique and the fourth bridge arm uses fully compensated control method. The inverter can maintain a symmetrical output voltage when the proposed scheme under the unbalanced load.

Research of Mining STATCOM Based on Hybrid Multilevel H-bridge Inverter

The paper presents a new STATCOM system based on H-bridge inverter. It can be used in mine power network. It has been commonly verified for the positive effects of SVG on the reactive power compensation and voltage fluctuation suppression. This paper focuses on a generalized structure of multilevel power converter where individual voltage sources are not necessarily the same. The cascade H-bridge consists of two cells, high-voltage cell and low-voltage cell. The high-voltage cell is responsible for voltage lifting, while the low-voltage cell is responsible for PWM modulation. If two cells are cascaded with DC voltages in a ratio of 2:1, the single-phase output voltage can reach 7 levels. Increasing voltage levels of output waveform can bring up AC current quality, optimize harmonic spectrum and enhance converter efficiency. The hybrid multilevel is characterized by per-phase series connection of a high-voltage H-bridge converter and a low-voltage H-bridge converter. Due to the different capacitor voltage, it is a key problem as to how to maintain the capacitor’s voltage at a reference level. Independent DC source can effectively ensure the DC voltage. Through the reactive power compensation technology, the three-phase voltage and current can remain at the same phase.

THD Analysis of Cascaded H-Bridge Inverter with Fuzzy Logic Controller

In recent days, the multilevel inverter technology is widely applied to domestic and industrial applications for medium voltage conversion. But, the power quality issues of the multilevel inverter limit the usage of much sensitive equipment like medical instruments. The lower distortion level of the output voltage and current can generate a quality sinusoidal output voltage in inverters and they can be used for many applications. The harmonics can cause major problems in equipments due to the nonlinear loads connected with the power system. So, it is necessary to minimize the losses to raise its overall efficiency. In this paper, a new topology of seven level asymmetrical cascaded H-bridge multilevel inverter with a Fuzzy logic controller had been implemented to reduce the Total Harmonic Distortion (THD) and to improve the overall performance of the inverter. The proposed model is well suited for use with a solar PV application. In this topology, only six IGBT switches are used with three different voltage ratings of PV modules (1:2:4). The lower number of semiconductor switches leads to minimizing overall di/dt ratings and voltage stress on each switches and switching losses. The gate pulses generated by Sinusoidal Pulse Width Modulation (SPWM) technique with a Fuzzy logic controller are also introduced. A buck-boost converter is used to maintain the constant PV voltage level integrated by an MPPT technique followed by Perturb and Observer algorithm is also implemented. The MPPT is used to harness the maximum power of solar radiations under its various climatic conditions. The new topology is evaluated by a Matlab/Simulink model and compared with a hardware model. The results proved that the THD achieved by this topology is 1.66% and realized that it meets the IEEE harmonic standards.

The improved PAC method for a three-phase PWM grid-connected inverter

In this paper, a vector regulating principle of the phase and amplitude control PAC method for three-phase grid-connected inverters is presented.To solve the problem of heavy inrush current and slow dynamic response when system starts up, the starting voltage prediction control and the current feed-forward control are proposed and used, which improve the dynamic performance of the system in the PAC.The experimental results carried out on a three-phase grid-connected inverter proved the validity of the proposed method.

Capacitor Pattern H-Bridge Multilevel Inverter (CPHMLI) Using Phase Diposition Pulse Width Modulation for Grid Applications

This work presents an implementation of an innovative single phase multilevel inverter using capacitors with reduced switches. The proposed Capacitor pattern H-bridge Multilevel Inverter (CPHMLI) topology consists of a proper number of Capacitor connected with switches and power sources. The advanced switching control supplied by Pulse Width Modulation (PDPWM) to attain mixed staircase switching state. The charging and discharging mode are achieved by calculating the voltage error at the load. Furthermore, to accomplish the higher voltage levels at the output with less number of semiconductors switches and simple commutation designed using CPHMLI topology. To prove the performance and effectiveness of the proposed approach, a set of experiments performed under various load conditions using MATLAB tool.

Realization of a Nine-Level Cascaded NPC/H-Bridge PWM Inverter Using Phase-Shifted Carrier PWM Technique

Cascaded H-Bridge inverter has been researched for the past two decades, but there are no explicit guidelines on how one can realize a cascaded NPC （neutral-point-clamped）/H-Bridge inverter. Past research has also concentrated on realizing a five-level NPC/H-Bridge inverter. This fails to address the principle of realizing a general cascaded N-level NPC/H-Bridge PWM inverter. This paper proposes an improved topology for achieving a nine-level cascaded NPC （neutral-point-clamped） H-Bridge inverter with reduced harmonic content. This new proposed topology requires a lesser number of separate dc sources as compared to conventional cascaded H-Bridge inverter. The whole system is considered as having four three level legs having two positive and two negative legs. By properly phase shifting the modulating wave and carriers, a nine-level output is achieved. A theoretical harmonic analysis of the proposed inverter is carried out based on double Fourier principle. The theoretical results are verified through MATLAB simulation.

Finite Set-Model Predictive Current Control of Three-Phase Voltage Source Inverter for RES （Renewable Energy Systems） Applications

This paper focuses on a combination of three-phase VSI （voltage source inverter） with a predictive current control to provide an optimized system for three-phase inverters that control the load current. A FS-MPC （finite set-model predictive control） strategy for a three-phase VSI for RES （renewable energy systems） applications is implemented. The renewable energy systems model is used in this paper to investigate the system performance when power is supplied to resistive-inductive load. With three different cases, the evaluation of the system is done. Firstly, the robustness of control strategy under variable DC-Link is done in terms of the THD （total harmonic distortion）. Secondly, with one prediction step, the system performance is tested using different sampling time, and lastly, the dynamic response of the system with step change in the amplitude of the reference is investigated. The simulations and result analyses are carried out using Matlab/Simulink to test the effectiveness and robustness of FS-MPC for two-level VSI with AC filter for resistive-inductive load supplied by a renewable energy system.

Topological Comparison and Analysis of Medium-voltage and High-power Direct-linked PV Inverter

Among all the renewable energy sources,the installed capacity of solar power generation is the fastest growing in recent years,so photovoltaic(PV)power generation still has great market potential.Compared with low-power systems,large-scale PV systems are more commercially attractive,because they can reduce the cost of the system per watt.The PV inverters with centralized and string structure have been applied in large-scale PV plant,but it is difficult to further increase the voltage and power levels for a single converter.In addition,the line-frequency isolation transformer requires a large amount of materials and has a large volume and weight.Therefore,it is a current trend for large-scale PV system to increase the voltage and power levels to directly connect to the medium-voltage power grid.Based on this,this paper investigates and compares several topologies of PV inverters without line-frequency transformer,including the MMC structure and the three-phase cascaded H-bridge(CHB)structure,which are able to directly connect to the 35kV medium-voltage power grid,and can not only make the voltage and power levels higher,but also further reduce the cost and volume of the whole system.

Evaluation of 1.2 kV SiC MOSFETs in Multilevel Cascaded H-bridge Three-phase Inverter for Medium-voltage Grid Applications

A study is conducted to evaluate 1.2 kV silicon-carbide(SiC)MOSFETs in a cascaded H-bridge(CHB)three-phase inverter for medium-voltage applications.The main purpose of this topology is to remove the need for a bulky 60 Hz transformer normally used to step up the output signal of a voltage source inverter to a medium-voltage level.Using SiC devices(1.2-6.5 kV SiC MOSFETs)which have a high breakdown voltage,enables the system to meet and withstand the medium-voltage stress using only a minimal number of cascaded modules.The SiC-based power electronics when used in the presented topology considerably reduce the complexity usually encountered when Si devices are used to meet the medium-voltage level and power scalability.Simulation and preliminary experimental results on a low-voltage prototype verifies the nine-level CHB topology presented in this study.

Robust Dichotomy Solution-Based Model Predictive Control for the Grid-Connected Inverters with Disturbance Observer

This paper proposes a robust dichotomy-based model predictive control(DS-MPC)with a fixed switching frequency for the grid-connected inverter(GCI).The proposed fast dichotomy algorithm can select and deduce the optimal voltage vector dynamically through the space vector plane.Therefore,the proposed DS-MPC strategy could ensure dynamic performance and steady-state performance as well.Also,the current control robustness can be improved through DS-MPC with disturbance observer(DO)based on the extended Kalman filter(EKF).The novelty of this control is that the current control with fast dynamic response can be realized in the weak grid,even if the grid voltages are greatly distorted.Simulation and hardware experiments on the weak grid validate the effectiveness of the proposed DS-MPC with the EKF observer approach.

A New Structure of Multilevel Inverter with Reduced Number of Switches for Electric Vehicle Applications

Both Hybrid Electric Vehicles (HEVs) and Electric Vehicles (EVs) need a traction motor and a power in-verter to drive the traction motor. The requirements for the power inverter include high peak power, opti-mum consumption of energy, low output harmonics and inexpensive circuit. In this paper, a new structure of multilevel inverter with reduced number of switches is proposed for electric vehicle applications. It consists of an H-bridge and an inverter in each phase which produces multilevel voltage by switching the dc voltage sources in series. As the number of switches are reduced, both conduction and switching losses will be de-creased, which leads to increase the efficiency of converter. The size and power consumption of driving cir-cuits are also reduced. The proposed three phase inverter can produces more number of voltage levels in the same number of the voltage source and reduced number of switches compared to the conventional inverters. This structure minimizes the total harmonic distortion (THD) of the output voltage waveforms. The structure of proposed multilevel inverter, modulation method, switching losses, THD calculation and simulation re-sults with PSCAD/EMTDC software are shown in this paper.

Neural Network and Fuzzy Control Based 11-Level Cascaded Inverter Operation

This paper presents a combined control and modulation technique to enhance the power quality(PQ)and power reliability(PR)of a hybrid energy system(HES)through a single-phase 11-level cascaded H-bridge inverter(11-CHBI).The controller and inverter specifically regulate the HES and meet the load demand.To track optimum power,a Modified Perturb and Observe(MP&O)technique is used for HES.Ultra-capacitor(UCAP)based energy storage device and a novel current control strategy are proposed to provide additional active power support during both voltage sag and swell conditions.For an improved PQ and PR,a two-way current control strategy such as the main controller(MC)and auxiliary controller(AC)is suggested for the 11-CHBI operation.MC is used to regulate the active current component through the fuzzy controller(FC),and AC is used to regulate the dc-link voltage of CHBI through a neural network-based PI controller(ANN-PI).By tracking the reference signals fromMC and AC,a novel hybrid pulse widthmodulation(HPWM)technique is proposed for the 11-CHBI operation.To justify and analyze the MATLAB/Simulink software-based designed model,the robust controller performance is tested through numerous steady-state and dynamic state case studies.

Dual-loop Control Strategy for Grid-connected Inverter with LCL Filter

As to the concrete topology of three-phase LCL type grid-connected inverter with damping resistance, mathematical model was deduced in detail, using method of equivalent transformation to the structure diagram, damping resistance was virtualized, mathematical model under the DQ frame that can realize decoupling control was established, a dual-loop control strategy for grid-connected inverter with LCL filter was proposed, the system stability was analyzed and the design method of controller was given. The proposed method overcame the flaws of loss increase, efficiency reduce and cost increase which were caused by damping resistance in LCL type grid-connected inverter, the system efficiency and power supply quality of the output were improved. Feasibility and effectiveness of the new method were validated by simulation and experimental results.